1. Field of the Invention
The, present invention relates to an engine lubrication system for supplying the oil, inside an oil pan which is joined to the lower part of an engine block, the engine block supporting a crankshaft in the vertical direction, to an area that is to be lubricated by means of an oil pump.
2. Description of the Related Art
Japanese Utility Model Registration Application Laid-open No. 64-25415 discloses a system in which the oil, inside an oil pan joined to the lower face of the engine block of a vertical engine, is drawn off by means of an oil pump provided on the lower end of a camshaft and supplied to each area that is to be lubricated via an oil supply passage. The oil supply passage is provided with a relief valve, and when the pressure of-the oil discharged by the oil pump becomes excessive, the relief valve opens to return-the oil in the oil supply passage, to the oil pan.
Furthermore, Japanese Patent Application Laid-open No. 1-267307 discloses a system in which an oil pan is joined to the lower face of the engine block of a vertical engine via a bearing case, and an oil pump is provided on the bearing case.
With regard to the above-mentioned system disclosed by Japanese Utility Model Registration Application Laid-open No. 64-25415, since the excess oil is directly discharged into the upper space of the oil pan via the oil supply passage when the relief valve opens, the oil dropping down from the relief valve above, makes the oil inside the oil pan foam, and there is a possibility that the oil that is drawn off from the oil pan via the oil pump could thereby be contaminated with air bubbles, thus degrading the lubrication performance.
With regard to the above-mentioned system disclosed by Japanese Patent Application Laid-open No. 1-267307, since the oil pump is placed between the engine block and the oil pan, in order to secure a space for placing the oil pump that is sufficient for the external size of the pump, it is necessary to provide space between the engine and the surrounding structure in the horizontal direction and, in particular, in the vertical direction, and there is the problem that the size of engine compartment increases.
The present invention has been carried out in view of the above-mentioned circumstances, and it is an object of the present invention to reduce the space required for a vertical engine, particularly in the vertical direction, and to prevent bubble formation in the oil inside the oil pan due to the oil discharged by the relief valve via the oil supply passage.
In accordance with a first characteristic of the present invention in order to achieve the above-mentioned object, there is proposed an engine lubrication system comprising an oil pan joined to the lower part of an engine block, the engine block supporting a crankshaft in the vertical direction. An oil pump draws off oil, stored in the oil pan via an oil inlet passage and supplies the oil to an area that is to be lubricated via an oil supply passage. A relief valve is provided for discharging excess oil discharged from the oil pump via the oil supply passage. The oil pump is placed outside the oil pan and is driven by a camshaft, and the relief valve is placed inside the oil pan. The oil supply passage and oil inlet passage are communicated with each other via a connecting path by opening the relief valve.
In accordance with the above-mentioned arrangement, since the oil pump is placed outside the oil pan and driven by the camshaft and the relief valve is separated from the oil pan and placed inside the oil pan, the space needed for placing the oil pump and the relief valve can be divided into two spaces. By so doing, the space needed for the engine particularly in the vertical direction can be reduced in comparison with the case where a large-sized oil pump including an integral relief valve is driven by a camshaft or crankshaft and, in particular, with regard to the engine for an outboard motor which is mounted on a supporting face close to the bottom of the engine compartment, the size of the engine compartment can be reduced. Furthermore, when the relief valve provided in the oil supply passage for supplying oil from the oil pump to an area that is to be lubricated, opens, since the oil passing through the relief valve from the oil supply passage is not returned directly to the oil pan but it is returned to the oil inlet passage extending from the oil pan to the oil pump via the connecting path, it is possible to prevent bubble formation in the oil inside the oil pan due to the oil discharged from the relief valve. It is thus possible to prevent bubble contamination of the oil drawn off from the oil pan by the oil pump and to reliably lubricate an area that is to be lubricated.
In accordance with a second characteristic of the present invention, in addition to the above-mentioned first characteristic, an engine lubrication system is proposed, wherein an oil passage formation member, to which a suction pipe extending inside the oil pan, drawing off oil, and supplies the oil to the oil pump is connected, is fixed in a detachable manner to the lower face of the engine block. The oil inlet passage, the relief valve and the connecting path are provided in the oil passage formation member.
In accordance with the above-mentioned arrangement, since the oil inlet passage, the relief valve and the connecting path are provided in the oil passage formation member that is fixed in a detachable manner to the lower face of the engine block, and the suction pipe is connected to the oil passage member, the suction pipe and the relief valve can be assembled merely by fixing the oil passage formation member to the lower face of the engine block without subjecting the engine block to any special processing, thus contributing to a reduction in the number of assembly steps. Moreover, by forming the oil inlet passage, relief valve and connecting path into an assembly that also provides a connection part for the suction pipe, the number of parts and the cost can be reduced.
Oil passage p0 and oil chamber r1 in the embodiment below correspond to the oil inlet passage and oil supply passage respectively of the present invention.